Excerpt from "'Should I Buy It?' - Ice Breaker & Other Exotics" (Jan. 16th, 2015)
Yes, you should buy Ice Breaker immediately. No question.
Ice Breaker is one of the most critical weapons for a Guardian to own in PVE. Why? Ammo regeneration. It starts with 0 ammo, but generates 1 shot per ~4 to 5 seconds. If you're burning through a full clip of 6, you'll get 7-8 shots off before needing to switch/wait. Even better? You can use Ice Breaker to generate ammo for another Special Weapon. Equip it until the clip reaches 6, then switch; it won't give you much, but it can make a huge difference.
As if you needed another reason, its main talent causes kills to explode. It's similar to the Firefly talent, but doesn't need a precision kill. Extremely satisfying on clouds of Thrall. For bosses, we now prefer Black Hammer – but we all know Ice Breaker is the original infinite ammo Solar sniper.
"Downsides": Can't pick up ammo. Max clip of 6. Kicks like a mule.
PVP: It's not the best for PVP. Low Rate of Fire. Worst-in-class Stability (24). Start with 0 ammo on-spawn. Even though it does great damage on body shots, you'll frequently prefer a Sniper Rifle with a quicker Rate of Fire. Upside: with a Defender's Weapons of Light, you can get one-hit body shots.